There are two leading theories about where the rock, called "Pinnacle Island," came from.

The most likely scenario is that Opportunity flicked the rock with one of its wheels.

"We had driven a meter or two away from here, and somehow maybe one of the wheels, kind of, managed to spit it out of the ground, and have it slide to this position," [lead scientist of the Mars Exploration Rover mission Steve] Squyres said.

Alternatively, there could be a smoking hole in the ground nearby and the rock could be a piece of crater ejecta, or piece of matter spewn from the impact of a meteorite. Squyres doesn't think this is as likely as the idea that the rover displaced the rock, however.

"We're completely confused, we're having a wonderful time, everyone on the team is arguing and fighting," Squyres said.

I dunno, it looks kinda like a crushed beer can. I suspect that little trash compactor WALL-E had something to do with this. When reached for comment, he had this to say: "Eva." And that's pretty much all he said -- he just kept repeating it, OVER and OVER and OVER. He sounded drunk, I think she might have left him for one of those new Roomba floor scrubbers.

Thanks to E V I L A R E S, ChaosLex and E.N., who are all convinced it's a teensy alien spacecraft. That was my second guess.